The pope has sparked controversy by saying defending heterosexuality is as important as saving the world's rainforests from destruction.

Speaking in a holiday address to the Curia, the Vatican's central administration, Benedict said yesterday the church viewed the distinction between men and women as central to human nature, and "asks that this order, set down by creation, be respected".

The church, he said, "should protect man from the destruction of himself. A sort of ecology of man was needed, he said," adding: "The tropical forests do deserve our protection; but man, as a creature, does not deserve any less."

Benedict focused his attack on what he described as "gender" theories, "which lead towards the definitive emancipation of man from creation and the creator".

Homosexual groups in Italy called the speech an unfounded attack on homosexuality and, more specifically, on people who undergo sex changes. "What keeps the pope awake at night is the idea that human beings might be able to seek out their own sexual identity in a bid to have a happy life," said Franco Grillini, head of Gaynet.

"The speech has no scientific basis," said Aurelio Mancuso, head of Arcigay. "A divine programme for men and women is out of line with nature, where the roles are not so clear."

The Catholic church teaches that while homosexuality is not sinful, homosexual acts are. It opposes gay marriage, and in October a leading Vatican official called homosexuality "a deviation, an irregularity, a wound".

Father Federico Lombardi, a Vatican spokesman, said today that the pope had not wished specifically to attack homosexuality or sex change operations in his speech. "He was speaking more generally about gender theories which overlook the fundamental difference in creation between men and women and focus instead on the role of cultural conditioning," he said.

Mike Egan, chair of the Lesbian and Gay Christian Movement, said: "It's all part of a fundamental mistake, to say that there's something abnormal about homosexuality. It's like being left-handed. There are much greater threats to marriage and family life.

"There are people among bishops and clergy who think the official line on homosexuality is not true and the more official pronouncements there are, the deeper the hole the church is digging for itself. I would say to gay Catholics, the man is right on lots of other things and hang on in there."

Catholic bishops in England and Wales are encouraging a more pastoral approach to homosexuals. Last month they issued a leaflet urging clergy and parishioners to welcome and respectful of gay men and lesbians. Its reading list did not include Vatican statements and omitted papal documents denouncing homosexuality.

The leaflet was called, "What is life like if you or someone in your family is gay or lesbian in their sexual orientation? ... and what can your parish family do to make a difference?" It acknowledged the "oppression" suffered by homosexuals.

"As a group that has suffered more than its share of oppression and contempt, the homosexual community has a particular claim on the concern of the church," it said.

The leaflet cited comments received during a survey suggesting that the church acknowledged it may have played a role in victimising and marginalising gay and lesbian Catholics. These included: "The continual message from the church is that homosexuality is so, so dreadful. Our gay son just hasn't stood a chance"; and, "My brother is gay; the church has been very intolerant of him."